1. Field
The following description relates to a high-efficiency magnetron and a high-frequency heating apparatus having the same.
2. Description of the Related Art
Generally, a magnetron is a device in which a flow of electrons is controlled under the influence of a magnetic field to generate extremely short radio waves. Such a magnetron is used in high-frequency heating apparatuses for cooking, such as microwave ovens, or other apparatuses, such as particle accelerators, radar, and the like.
The most common magnetron is a magnetron included in high-frequency heating apparatuses for cooking in homes or restaurants.
A conventional magnetron basically includes an anode unit surrounded by an outer yoke and a plurality of cooling fins, a cathode unit installed in the center of the anode unit, an output unit to radiate radio waves, an input unit for power input, and an upper magnet and a lower magnet installed respectively to the top and bottom of the anode unit to create a magnetic field in a working space between the anode unit and the cathode unit.
The anode unit includes a hollow anode cylinder, a plurality of vanes radially arranged around the center of the anode cylinder, and upper and lower pole pieces installed respectively to the top and bottom of the anode cylinder. The cathode unit includes a coil-shaped filament located in the center of the anode cylinder, and a center lead and a side lead to supply power to the filament.
The output unit includes an antenna lead having one end coupled to any one vane to outwardly transmit radio waves, and the input unit includes a plug to supply external power to the center lead and the side lead.
In the operation of the magnetron having the above-described configuration, when power is applied to the filament via the center lead and the side lead, a group of electrons is generated in the working space between the filament and the vanes. The group of electrons is spirally rotated under the influence of a strong electric field and a magnetic field created in the working space, causing radio waves to be directed to the vanes. Then, the radio waves are discharged outward via the antenna lead.
The conventional magnetron does not consider load variation, i.e. load characteristics represented as a Ricke diagram. Thus, the magnetron may achieve high efficiency under matched load causing no reflection from load of output microwave power, but may fail to achieve high efficiency due to low oscillation efficiency under mismatched load causing reflection, e.g., in a microwave oven.
In addition, development of higher efficiency and more energy saving magnetrons having a smaller tube body causes deterioration of load stability (MoB) that is an index of stable magnetron operation, which makes it impossible to maintain stable oscillation.
Moreover, to restrict unwanted harmonic noise, the output unit of the magnetron includes at least one metal cylinder coaxial with the antenna lead to construct a λ/4 type choke structure having a ¼ depth of a frequency wavelength to be restricted. However, resistance of a skin based on skin effect, determined by permeability, resistivity, and frequency of a material, causes deterioration of resonance sharpness (Q) of the λ/4 type choke structure and insufficient restriction of harmonic noise. Thus, the magnetron may be unsuitable because it does not satisfy noise standards, or may cause deterioration of microwave power of 2450 MHz due to reduced circuit efficiency caused by Joule loss (energy loss) in the metal cylinders of the λ/4 type choke structure, resulting in deterioration of oscillation efficiency.